Process for manufacturing a bipolar power transistor having a high breakdown voltage

Abstract

There is described a bipolar power transistor with high breakdown voltage, obtained in a heavily doped semiconductor substrate of the N type, over which a lightly doped N type layer, constituting a collector region of the transistor, is superimposed. The transistor has a base region comprising a heavily doped P type diffusion, which extends into the lightly doped N type layer from a top surface. The transistor further includes an emitter region constituted by a heavily doped N type diffusion extending from the top surface within said heavily doped P type diffusion. The heavily doped P type diffusion is obtained within a deep lightly doped P type diffusion, extending from said top surface into the lightly doped N type layer and formed with acceptor impurities of aluminum atoms.

What is claimed is: 
     
       1. A process for manufacturing a bipolar power transistor having a high breakdown voltage, the process comprising the steps of: a) growing a lightly doped N type epitaxial layer over a heavily doped semiconductor substrate of the N type;   b) growing oxide over a top surface of said lightly doped N type epitaxial layer;   c) masked implanting of aluminum atoms into said lightly doped N type epitaxial layer;   d) drive-in diffusing said aluminum atoms into said lightly doped N type epitaxial layer to form a lightly doped P type base region;   e) masked implanting of a high concentration of acceptor dopants into said lightly doped P type base region;   f) drive-in diffusing said acceptor dopants into said lightly doped P type base region to obtain a heavily doped P type base region within said lightly doped P type base region;   g) masked implanting of a high concentration of donor dopants into said heavily doped P type base region; and   h) drive-in diffusing said donor dopants into said heavily doped P type base region to obtain a diffused heavily doped emitter region.   
     
     
       2. The process according to claim 1, further including the step of forming a plurality of P type aluminum-doped concentrical rings around and simultaneously to said lightly doped P type base region. 
     
     
       3. The process according the claim 2, wherein the step of forming ensures that said rings have a dopant concentration which diminishes going from a most internal ring to a most external ring. 
     
     
       4. The process according to claim 3, characterized in that said rings with dopant concentration which diminish going from a most internal ring to a most external ring are formed by implanting said aluminum atoms through annular windows in a mask layer having decreasing area going from said most internal ring to said most external ring, to progressively decrease a total amount of aluminum atoms implanted into the N type epitaxial layer going from the most internal ring to the most external ring. 
     
     
       5. The process according to claim 1, wherein said acceptor dopants are ions of boron. 
     
     
       6. A method for manufacturing a bipolar power transistor, the method comprising the steps of: a) growing a collector region on a semiconductor substrate;   b) growing an oxide on a top surface of the collector region;   c) implanting impurity atoms into the collector region via a first mask;   d) drive-in diffusing the impurity atoms into the collector region to form a first portion of a base region in the collector;   e) implanting a concentration of dopants into the first portion of the base region via a second mask:   f) drive-in diffusing the dopants to form a heavily doped second portion of the base region within but not extending through the first portion;   g) implanting a concentration of dopants of a second type into the second portion via a third mask; and   h) drive-in diffusing the dopants of the second type into the second portion of the base region to obtain a heavily doped emitter region.   
     
     
       7. The method of claim 6, further including the step of forming a plurality of concentrical rings around the first portion of the base region, each ring being of a similar semiconductor type as the first portion, and each ring having a dopant concentration that diminishes as the rings extend outwardly from the first portion. 
     
     
       8. The method of claim 7 wherein the step of forming a plurality of concentrical rings is done simultaneously with step (d). 
     
     
       9. The method of claim 8 wherein the first mask has openings to form each ring, and inner rings having a larger opening than a subsequent outer ring. 
     
     
       10. The method of claim 6 wherein: the semiconductor substrate has a diffusivity; and   step (c) includes implanting impurity atoms having a high diffusivity in relation to the diffusivity of the semiconductor substrate.   
     
     
       11. The method of claim 10 wherein the impurity atoms are aluminum. 
     
     
       12. The method of claim 6, wherein step e) includes implanting boron atoms into the first portion of the base region. 
     
     
       13. The method of claim 6, wherein: step c) includes implanting an amount of impurity atoms so that step d) results in a first concentration of impurity atoms in the first portion of the base region;   step e) includes implanting an amount of dopants so that step e) results in a second concentration of dopants in the second portion of the base region that is greater than the first concentration of impurity atoms in the first portion of the base region.   
     
     
       14. A method for manufacturing a bipolar power transistor, comprising the steps of: forming a collector region in a substrate;   forming a first diffused portion of a base region adjacent the collector region, the first diffused portion having a first concentration of impurities of a first type;   subsequently forming a second diffused portion of the base region within the first diffused portion, the second diffused portion having a second concentration of impurities of the first type, the second concentration being greater than the first concentration; and   forming an emitter region within the second diffused portion of the base region.   
     
     
       15. The method of claim 14, wherein the step of forming a second diffused portion includes forming the second diffused portion so that the first diffused portion remains adjacent the collector region. 
     
     
       16. The method of claim 14, wherein the step of forming the first diffused portion includes forming the first diffused portion with acceptor impurities. 
     
     
       17. The method of claim 16, wherein the step of forming the first diffused portion includes forming the first diffused portion with aluminum atoms. 
     
     
       18. The method of claim 14, wherein the step of subsequently forming a second diffused portion includes forming the second diffused portion with boron. 
     
     
       19. The method of claim 14, further comprising a step of forming a plurality of concentric rings about the first portion of the base region, each ring having impurities of the first type and having a respective dopant concentration, wherein the dopant concentration in each ring is less than a dopant concentration of any rings closer to the first portion. 
     
     
       20. The method of claim 14, wherein the step of forming the first diffused portion includes the steps of: implanting a first dose of impurities of the first type via a first mask; and   diffusing the first dose of impurities.   
     
     
       21. The method of claim 20, wherein the step of subsequently forming the second diffused portion includes the steps of: implanting a second dose of impurities of the first type via a second mask that is different from the first mask; and   diffusing the second dose of impurities.